The burgeoning field of minimally invasive medical procedures (MIMPs) has increased the demand for systems that produce less tissue damage and trauma, faster recovery times, and lower risks to the patient. Ideally, the practitioner of MIMPs requires smaller instruments that perform a greater variety of functions. Furthermore, a “one-instrument-does-all” approach must add simplicity, not complexity, by ensuring that it is easy to use, minimizing the time required to master its operation.
The instruments used by practitioners of MIMPs typically include several different discrete systems for optical imaging, monitoring, maneuvering, sizing, diagnosis, biopsy, therapy, surgery, and non-visual monitoring/sensing. It clearly is preferable to combine the functions provided by these instruments in a single compact device to reduce the number of surgical ports that are currently required for a plurality of single-function tools, each providing only a single one of these functions. By employing an integrated multi-functional tool so that only one small port is used, the risks associated with repeatedly removing and inserting surgical tools can be dramatically reduced. Since most MIMPs require the practitioner to constantly monitor the procedure visually, optical imaging to identify a specific site to next render therapy or to view the results of the therapy already rendered is considered a requirement for any fully integrated system for MIMPs. Thus, an appropriate multifunction instrument will most likely include an optical imaging system, and the imaging system should be integrated with one or more diagnostic, imaging, and/or therapeutic tools.
At present, the tools commonly used for MIMPs cannot readily be integrated into a single device without increasing the size of the resultant instrument to an excessive degree. For example, all commercial optical imaging systems that include a maneuverable flexible shaft must maintain a certain size (diameter) in order to preserve image quality. Currently, flexible scopes cannot be made smaller than this limit unless image field of view (FOV) or resolution is sacrificed. Although imaging and some diagnostic capability can be integrated into existing scopes now in use, such as standard tissue imaging in combination with fluorescence for early detection of cancers, the optical systems of current flexible scopes cannot provide integrated diagnoses and therapies at the required degrees of performance, size, and price that will be demanded in the future by medical practitioners.
Current Technology Used for MIMPs
Flexible scope designs that are now commercially available use either a bundle of optical fibers (optical waveguides) and/or one or more cameras having an array of detectors to capture an image. Thus, the diameter of these flexible scopes employed for remote imaging cannot be reduced to smaller than the image size. Ignoring the optical fibers used for illumination, the scope diameter is therefore limited by the individual pixel size of a camera or by the diameter of optical fibers used to acquire the image. Currently, the smallest pixel element is determined by the size of the end of an optical fiber, which has a minimum core diameter of about 2 μm. To propagate light through an optical fiber, a surrounding cladding layer is required, increasing the minimum pixel size to more than 3 μm in diameter. If a standard VGA image is desired (e.g., with a resolution of 640×480 pixels), then a minimum diameter required for just the image optical fiber is more than 2 mm. Therefore, resolution and/or FOV must be sacrificed by having fewer pixel elements in order to achieve scopes with less than 2 mm overall diameter. All commercially available scopes suffer from this fundamental tradeoff between high image quality and small size.
Thus, it would be desirable to add diagnostic, monitoring, and therapeutic (or optical surgical) capability to a remote imaging system for the purpose of reducing the overall size of the instrument used for MIMPs. Since, for the reasons noted above, the current design for flexible scopes cannot readily be reduced in size without reducing imaging performance, the options for integrating diagnostic and therapeutic applications with an imaging system would appear to require an increase in the size of the instrument or use of separate instruments for each function. For example, a high intensity light source might be added to a general endoscopic surgical system to carry out photodynamic therapy (PDT) or laser surgery, or a polarized light source or other multi-spectral specialty light sources might be needed for diagnosis and/or sensing a condition of an ROI. However, the white light illumination for standard endoscopic imaging is typically provided through an optical fiber bundle that diffusely illuminates the tissue and is incapable of providing a directed optical energy at high intensity and resolution to produce effective optical therapies, and will often not have the characteristics required for diagnostic processes. Therefore, any optical therapies that require directed illumination of high intensity light, such as PDT and laser surgery, or any diagnostic processes that also require a special light source cannot use existing optical designs for flexible imaging scopes, but instead, must rely on a second optical pathway and separate control mechanisms.
To perform diagnostic or therapeutic MIMPs, one or more separate instruments are used within the FOV of a standard endoscopic imager, and any additional separate instrument often must be held and maneuvered by a second medical practitioner. Typically, the second instrument provides a high intensity point source of light for optical therapies, a hot-tipped probe for thermal therapies, or a trocar used for mechanical cutting. The second instrument is moved to the surface of the tissue and usually moved within or across the surface of the tissue, covering the area of interest as the tool is scanned and manipulated by hand. These secondary instruments are inserted into the patient's body through a separate port, and thus, while being used, are viewed from a different point of view in the visual image. Furthermore, the therapeutic instrument often blocks the practitioner's direct view of the ROI with the imaging tool, making highly accurate therapies quite difficult for the medical practitioner to achieve. Significant amounts of training and practice are required to overcome these difficulties, as well as the capability to work with a reduced sense of touch that is conveyed through the shaft of an instrument having friction and a non-intuitive pivot at the point of entry. Thus, to work effectively with current imaging and therapeutic technologies, the practitioner of MIMPs must be highly trained and skilled.
Clearly, there is a need for an instrument that integrates imaging, diagnostic, and therapeutic functions, delivers these functions through a relatively small diameter, and is sufficiently intuitive to use as to require little training or skill. Ideally, the instrument should be implemented using a single optical fiber, but should still be capable of providing a sufficient FOV, good image size, and resolution, and should ensure that the ROI within a patient's body while administering therapy corresponds to that during imaging. Currently, none of the instruments commercially available provide these capabilities and cannot be easily modified to provide such capabilities.
At least a partial solution to these problems has been developed, as disclosed in U.S. patent application Ser. No. 09/850,594 (this application was allowed and the Issue fee was paid more than one year ago, but the Letters Patent has not yet been issued). This application, which is entitled, “Medical Imaging, Diagnosis, and Therapy Using a Scanning Single Optical Fiber System” and which was filed on May 7, 2001, discloses how the distal end of a single optical fiber can be driven into a resonant or near resonant motion and used for providing imaging, monitoring, sensing, screening, diagnosis, and therapy for a region of interest in a patient's body. However, a problem arises when an attempt is made to add a therapeutic high-power laser light source to the scanning fiber endoscope of this earlier disclosure, so that the same optical fiber can be used for therapy provided by the high-power laser, as well as for imaging, optical diagnosis, and optical monitoring, during a MIMP.
There are two scenarios in which the same resonant optical fiber might be used for providing this combined functionality in a single compact device. In the first scenario, a single optical fiber is coupled to red, green, and blue (RGB) lasers for imaging, and is also selectively coupled to the high-power laser for providing therapy to a site. Following the teaching of the earlier patent application, the high-power laser would be energized only briefly to illuminate a single or few pixels for a very short dwell time, which as disclosed in this application, would be the same dwell time used for low-power laser light imaging with the RGB lasers, since the motion of the resonant optical fiber is not interrupted between the imaging a site and rendering therapy to the site. In this first scenario, the same single mode optical fiber for imaging is used for delivering the high-power pulse.
However, a substantial problem with this first approach is the short dwell time that is appropriate for the color imaging of tissue is fixed, but will typically be too short for the effective delivery of optical therapy. If the fixed dwell time is too short to perform the optical therapy using the laser power that can be delivered via the same single mode optical fiber, then an alternative approach is required. This alternative might require using additional optical fibers that only deliver therapeutic optical power to the tissue, separate from the resonant optical fiber scanner that is used for imaging, diagnostic, and/or monitoring functions. In this alternative, it is most likely that the separate optical fibers used for therapy would be non-scanning, creating fixed points of therapeutic illumination within the imaging field. If the therapeutic optical fibers are fixed in place, then the dwell times of high power laser illumination can extend as long as the therapeutic laser light source is energized, assuming that the endoscope can be held stationary with the high power laser light directed where desired at the site. Unfortunately, this second alternative approach increases the size and complexity of the endoscope and will probably not offer the option to readily scan the therapeutic optical fibers over a portion of the site to which the therapy is to be rendered. Fixed therapeutic optical fibers would require that the distal end of the endoscope be maneuvered to direct the high intensity light emitted from the distal end of the therapeutic optical fibers toward the desired treatment site. It would be preferable to develop a different way to render both therapy and one or more of the other functions of imaging, diagnosis, and monitoring using only a scanning optical fiber that would enable different dwell times for any one of these functions.
It would also be desirable to change the size of a scanned pattern, as well as its shape, and other characteristics, when providing any of the desired functions using a single scanning optical fiber. For example, a scanning pattern during imaging might image a substantially larger region compared to a relatively smaller portion of that region that should be scanned when delivering therapy, or doing an optical diagnosis. None of the earlier disclosure provided any technique for interrupting a scanning optical fiber to change functional modes and to change to the scanning characteristics that are appropriate for a specific function.
Since variable sequential framing provides imaging and one of diagnosis, therapy, and monitoring in time-series by using the same resonant scanning device, it is desirable to minimize the time required for the non-imaging function that occurs in a frame-sequential manner with the imaging function. In general, for therapy and some diagnoses, a shorter dwell time will reduce the localized heating and minimize optical damage to non-targeted tissue that may be caused by laser light directed at the tissue. However, shorter dwell times require higher peak power for the laser source, putting the light conductive medium at risk for optical damage. A specially conditioned light conductive medium assists in increasing the optical damage threshold and thus enables dwell times to be minimized. Because the risk for optical damage cannot be completely mitigated, it is desirable to monitor the ends of the light conductive medium for damage, so that the practitioner can avoid using the device when the light conductive medium is not functioning properly. Should the light conductive medium sustain damage, it will be necessary for the practitioner to replace the medium with a new one to restore the system functionality. Therefore the system should include means facilitating replacement of the light conductive medium in a manner that does not require a great amount of technical proficiency in coupling a light conductive medium to a light source. This goal can be achieved by including an automated positional control system with a software-based alignment routine that is independent of input by the user.
Another technique to reduce dwell times is the use of extrinsic chromaphores in the ROI. When applied by the practitioner, these chromaphores can assist in light absorption and thus localized heating, reducing the necessary dwell time of the applied light. The practitioner may want to use specific chromaphores for individual diagnostic or therapeutic procedures. Thus, it is desirable that a diagnostic or therapeutic system include contingencies for procedures involving the most often used chromaphores and fluorophores. These contingencies will very likely involve a variation of the dwell time in order to compensate for the chromaphore.
It is often necessary to monitor the progress of applied therapy in order to determine when the procedure is complete, since the time at which completion occurs may not be known to the practitioner beforehand. Previously used approaches have provided for image collection using fixed fiber detectors; however, there are other techniques that are useful in this situation. For example, collecting infrared radiation from the ROI can give a valuable clue to the temperature of the region. Monitoring the polarization of the light returned from the ROI can be a valuable in determining the state of the target of therapy. Time-of-flight measurements can give specific information as to the depth or distance of the ROI from the distal tip of the scope. Thus, in at least one embodiment a surgical scope should have the ability to monitor the progress of applied therapy by collecting feedback from the ROI.